Magnetic isotope effect of magnesium in phosphoglycerate kinase phosphorylation.

Phosphoglycerate kinase (PGK) is found to be controlled by a (25)Mg(2+)-related magnetic isotope effect. Mg(2+) nuclear spin selectivity manifests itself in PGK-directed ADP phosphorylation, which has been clearly proven by comparison of ATP synthesis rates estimated in reaction mixtures with different Mg isotopy parameters. Both pure (25)Mg(2+) (nuclear spin 5/2, magnetic moment +0.85) and (24)Mg(2+) (spinless, nonmagnetic nucleus) species as well as their mixtures were used in experiments. In the presence of (25)Mg(2+), ATP production is 2.6 times higher compared with the yield of ATP reached in (24)Mg(2+)-containing PGK-based catalytic systems. The chemical mechanism of this phenomenon is discussed. A key element of the mechanism proposed is a nonradical pair formation in which (25)Mg(+) radical cation and phosphate oxyradical are involved.